Structure and biomimetic, electrochemically-mediated semisynthesis of the novel pentacyclic indole danuphylline

Abstract

The structure of the novel pentacyclic indole, danuphylline, from Kopsia dasyrachis was established by spectral analysis. Anodic oxidation of the hexacylic alkaloid methyl 11,12-methylenedioxychanofruticosinate on platinum in TEAP/MeCN-CH2Cl2 (2 F mol-1) yielded an iminium ion salt which on silica gel chromatography underwent a facile retro-aldol process to give danuphylline. Allowing the oxidation to proceed until consumption of 4 F mol-1 of charge resulted in an unprecedented electrochemically-mediated aromatic chlorination yielding 10-chloro-danuphylline.